Conventionally, in order to purify blood of patients with renal function insufficiency, for example, medical treatments using Continuous Hemofiltration (CHF), Continuous Hemodiafiltration (CHDF), and/or the like have been performed.
In the CHF, blood taken from a patient is provided to a blood is purifier having a semipermeable membrane (hemofiltration membrance) for hemofiltration, and then filtered by the hemofiltration membrane to generate purified blood. The purified blood is returned to the patient body, and waste products (electrolytic substance such as urea and sodium chloride, for example) and solvent (water) resulting from the hemofiltration are discarded. In parallel, a predetermined replacement fluid is supplied to blood of the patient so as to supplement a decrease in solvent of the blood. The above processing is performed continually and slowly. In the CHF, waste products and solvent which are taken from blood in order to be discarded are called filtrate.
On the other hand, the CHDF is a method of improving a capability of removing small molecules in the CHF. In the CHDF, dialysis as well as the CHF are performed. More specifically, in the CHDF, a blood purifier having a dialysis membrane in addition to a hemofiltration membrane is used. The blood purifier is provided also with dialysate. Waste products still included in the purified blood after hemofiltration are sent to the dialysate through the dialysis membrane, so that the waste products can be removed from the blood. Then, the blood purified by the hemofiltration and the dialysis is as returned to the patient body and a replacement fluid is supplied to the blood of the patient. The above processing is performed continuously and slowly. In the CHDF, waste product and solvent which are taken from the blood during hemofiltration, and used dialysate are called filtrate.
In the meanwhile, a change in an amount of blood in a patient body affects patient's condition. In order to avoid such situations, it is necessary to keep a balance between (a) a flow rate of blood taken from the patient and (b) a total flow rate of blood returned to the patient and replacement fluid supplied to the patient. More specifically, it is necessary to continuously perform high-accuracy fluid control for 24 hours a day, so that a total amount of decrease in the dialysate and the replacement fluid is always equal to an amount of increase in the filtrate.
However, sending of the dialysate, the replacement fluid, and the filtrate required a plurality of pumps. If a difference of an amount of fluid sent by a single pump is 10%, a total difference of an amount of fluid sent by two pumps is 20% at maximum, for example. The difference is not allowable in treatments demanding the above-described fluid balance.
Therefore, there has been conceived a weight measuring apparatus that keeps, with high accuracy, balance between (a) a total amount of decrease in the dialysate and the replacement fluid and (b) an amount of increase in the filtrate, when the above-described blood purification treatment is performed (refer to Patent Reference 1, for example).
FIG. 10 is a diagram for explaining the conventional weight measuring apparatus.
As shown in FIG. 10, a blood purification apparatus 2 includes a conventional weight measuring apparatus 6 having a plurality of pumps 7 to 9. The pumps 7 to 9 send dialysate contained in a dialysate container 3, replacement fluid contained in a replacement fluid container 4, and filtrate contained in a filtrate container 5, respectively. The dialysate container 3, the replacement fluid container 4, and the filtrate container 5 are hanged by the weight measuring apparatus 6 to measure a total weight of the three containers. The pumps 7 to 9 are thereby controlled to keep a predetermined valued of the total weight.
Thereby, it is possible to control (a) a total amount of decrease in the dialysate and the replacement fluid and (b) an amount of increase in the filtrate to be equal to each other. In other words, in order to keep, with high accuracy, balance between (a) a total amount of decrease in the dialysate and the replacement fluid and (b) an amount of increase in the filtrate, the method of controlling the pumps 7 to 9 to keep the predetermined value of the total weight of the three containers is prefer to the method of measuring weights of the respective dialysate container 3, replacement fluid container 4, and filtrate container 5 and then controlling the pumps 7 to 9.